The invention lies in the automotive technology field. More specifically, the present invention relates to an injection device for an internal combustion engine using direct injection. The injection device includes, in general, an actuator, a piston, a compression chamber, a high-pressure line, an injection nozzle, a nozzle chamber, a nozzle spring chamber, a fuel supply line, and a pressure-relief valve.
Injection devices of that type are known, for example, from German published patent application DE 196 12 737 A1. In prior art injection devices, which are controlled in particular by solenoid valves, the initial injection, its metering and its delineation from the main injection are important parameters for influencing the noise or exhaust-gas emission. The minimum injected amount is thereby governed by the speed of operation of the solenoid valve. However, the injected amount, which is predetermined by the long travel of the solenoid valve, is often too great to allow combustion optimization. In the German application DE 196 12 737, a valve is provided in the flow path between the high-pressure chamber and a shut-off control line. The valve is closed at the start of injection and opens only as a function of the pressure in the high-pressure chamber in a small pressure range after the start of injection, releasing the flow path for a short period. This results in an injection pressure which remains constant for a short period and has an advantageous effect on the injection profile. However, the minimum injected amount is still not influenced by this.
The object of the invention is to provide an injection device for a direct-injection internal combustion engine which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and in which the initial injected amount can be reduced.
With the above and other objects in view there is provided, in accordance with the invention, an injection device for an internal combustion engine using direct injection, comprising:
an actuator and a piston connected to the actuator;
an injection device body-having a pressure chamber formed therein and a high-pressure line communicating with the pressure chamber;
an injection nozzle disposed in a nozzle chamber formed in the injection device body and communicating with a fuel supply line;
a pressure-relief valve disposed to communicate with the high-pressure line and to draw a constant volume of fuel from the high-pressure line upon closing.
In accordance with an added feature of the invention, the pressure-relief valve is disposed in a flow path between the fuel supply line and the pressure chamber.
In accordance with an additional feature of the invention, the pressure-relief valve comprises a piston movably disposed in a cylindrical bore, the bore having a first portion with a larger inner diameter and a second portion with a smaller inner diameter, and a conical step transition from the larger inner diameter to the smaller inner diameter; the piston having an upper, conically expanding segment and a ring segment below the upper segment, the ring segment sealing against an inner wall surface bounding the second portion of the bore, and wherein, during a downward movement of the piston, the conically expanding segment coming to be seated on the step transition.
In accordance with another feature of the invention, a lower segment of the piston, adjacent the ring segment, is formed with longitudinal grooves in an outer circumference thereof.
In accordance with again another feature of the invention, a lower segment of the piston, adjacent the ring segment, is formed with a central longitudinal hole and transverse holes adjacent thereto.
In accordance with a further feature of the invention, the fuel supply line opens into the cylindrical bore in a region of the lower segment of the piston.
With the above and other objects in view there is further provided, in accordance with the invention, an injection device for an internal combustion engine using direct injection, comprising:
an actuator;
a piston connected to the actuator;
an injection device body having a pressure chamber formed therein and a high-pressure line communicating with the pressure chamber;
an injection nozzle disposed in a nozzle chamber formed in the injection device body and communicating with a nozzle spring chamber and a fuel supply line; and
a pressure-relief valve disposed to draw a constant volume of fuel to the nozzle spring chamber upon closing, whereby the volume produces nozzle needle damping during opening of the injection nozzle.
It is thus possible to use a prior art pressure valve with constant-volume pressure relief for the pressure-relief valves, as is used for in-line injection pumps. It is thus possible to use a conventional type of pressure valve without any need for redesign.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a injection device for an internal combustion engine using direct injection, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.